I. Field of the Invention
The present invention relates to fluid systems and, more particularly, to a fluid device for indicating the rate of fluid flow through such system, and a new and improved means for biasing the indicator means towards a zero-flow position.
II. Prior Art
Positive displacement flow meters, such as described in my previous U.S. Pat. No. 3,282,102, issued on Nov. 1, 1966, impart a rotation to a shaft dependent upon the fluid flow through the flow meter. A pointer arm is secured to the end of the shaft externally of the flow meter and the pointer arm provides a visual indication of the rotation of the shaft and hence, the rate of flow through the flow meter.
The fluid flow responsive means, such as the vane in my aforementioned patent, is operatively connected with the shaft which is biased towards a zero-flow position. To achieve this end, previously known flow meters have utilized a torsion spring to bias the shaft, and hence the fluid flow measuring means connected therewith, towards a zero flow position. The previously known torsion spring biasing means, however, suffers from several disadvantages solved by the present invention. The most serious disadvantage of the previously known torsion spring biasing means is that the torsion spring is prone to failure from repetitive flexing. Such failure of the torsion spring not only necessitates expensive repair of the flow meter but also results in inaccurate flow meter readings until discovery of the torsion spring failure.
A second major problem incurred by the previously known torsion spring biasing means is that the rotation force transmitted to the shaft by the torsion spring varies over time due to fatigue of the spring. Spring fatigue produces increasingly inaccurate flow meter readings as time progresses and this inaccuracy is particularly noticable in low-flow flow meters.
Previously known indicator means for flow meters also frequently serve the additional function of activating an electrical switch when the fluid flow through the flow meter is relatively low. The electrical switch, in turn, activates electrical circuitry, and the like to energize a remote indicator or the like.
To achieve this function, previously known indicator means have included cam means operatively connected with the indicator shaft to actuate an electric switch when the rate of fluid flow reaches a predetermined condition. The previously known cam actuated switch means for flow indicators have proven to be somewhat unsatisfactory. Such switch assemblies are not only expensive to manufacture but, like the previously known torsion springs, are also prone to failure. Failure of the electric switch and/or its cam actuating means produces the serious consequence that substitution of a clean filter element for a dirty filter element will not occur thereby permitting a back up in the fluid system.